COF-based MMMs with light-responsive properties generating unexpected surface segregation for efficient SO2/N2 separation

The purification of sulfur dioxide (SO2) from the flue gas is an urgent problem given its toxicity to humans and organisms and attendant environmental concerns. In this study, aiming at the separation of SO2, mixed matrix membranes (MMMs) are fabricated by incorporating covalent organic framework (COF) into Pebax 1657 poly-mer matrix. By strengthening the solubility-diffusion mechanism of SO2 gas molecules, SO2/N2 gas separation performance is investigated. Firstly, MMMs are fabricated by incorporating a porous framework material (TpPa-1) containing SO2 affinity groups into the Pebax 1657 matrix as a filler. Then the azo group (Azo) is introduced into the MMMs by the method of physical blending. The MMMs with light-responsive characteristic are fabri-cated by introducing TpPa-1 blended with pAAB into the Pebax 1657 polymer matrix. Secondly, the SO2/N2 separation performance of Pebax/TpPa-1 MMMs is improved with the increasing of filler loading. Specially, the Pebax/TpPa-1 membrane with 5 wt% exhibits the most excellent SO2/N2 separation performance with SO2 permeability of 1709 Barrer and SO2/N2 selectivity of 811. The MMMs overcome the trade-off effect and achieve enhancement of SO2 permeability and SO2/N2 selectivity simultaneously. Thirdly, both the SO2 permeabilities and SO2/N2 selectivities of Pebax/pAAB@TpPa-1-5% membrane exhibit regular and reversible changes under UV-Vis light-conversion conditions, indicating that MMMs containing Azo possesses dynamic light-responsive properties. Furthermore, TpPa-1 and pAAB repel each other in the membrane because both have negative charges, resulting in the forced surface segregation of COF in the Pebax/pAAB@TpPa-1 MMMs.

Automated summary

In this study, mixed matrix membranes (MMMs) were fabricated by incorporating covalent organic framework (COF) into Pebax 1657 polymer matrix for the separation of sulfur dioxide (SO2). By strengthening the solubility-diffusion mechanism, the SO2/N2 gas separation performance was investigated. The Pebax/TpPa-1 membrane with 5 wt% filler loading exhibited the most excellent SO2/N2 separation performance with a permeability of 1709 Barrer and a selectivity of 811.